Thanks for all the responses!
So it seems that I'd be wasting my money buying the 70-300 non-L...
I do really want the 70-300L, but the only thing holding me back is the lens diameter. As I said, I do aviation photography and I need something that can fit through the fence.
I just went and took some photos last week with my 70-200, but they needed some intense post-processing to remove the fence links. Here's an example heavily manipulated to emphasize the problem I have with the wide L lenses:
I know the 70-300 L's diameter isn't as wide as the 70-200, but just how wide is it? Is it so wide that I'll still have these fence problems?
The 70-300L has an extending inner barrel when you zoom in. It is usually small enough to fit some fence. I shot this at the zoo through a fence: